Liquid crystal display devices, a type of display device, often have a lighting device because a liquid crystal panel itself does not emit light. In this case, the liquid crystal panel controls the transmission amount of light emitted from the lighting device in accordance with input image signals. Widely known systems of the lighting device include a direct backlight system in which a light source is disposed directly beneath a liquid crystal panel and an edge-lit (side-lit) backlight system in which a light guide plate is disposed directly beneath a liquid crystal panel and a light source is disposed lateral to the light guide plate. The edge-lit backlight system is often employed for small- to middle-sized liquid crystal display devices.
In an exemplary main configuration of a conventional edge-lit backlight, an LED substrate with light emitting diodes (LEDs), serving as light sources, linearly mounted thereon is disposed to face a side surface of a light guide plate. The light emitted from the LEDs enters from the side surface of the light guide plate to reach dots on the back surface of the light guide plate, so that the light is emitted from the surface facing the liquid crystal panel.
In a conventional edge-lit backlight, a different configuration may be added to the above main configuration or the main configuration may be partly changed. For example, Patent Literature 1 discloses a configuration including a reflection member that reflects light from LEDs to guide the light to a light incident surface of a light guide plate and contains a fluorescent material which is excited by light emission from the LEDs to become fluorescent to change the wavelength. According to Patent Literature 2, a light guiding member having a light diffusion part is provided in order to prevent unevenness of planar light from a light emitting surface of a light guide plate, and the light diffused by this light guide member is incident on the light guide plate.
Moreover, Patent Literature 3 discloses a planar light source device in which a light guide plate is used as in an edge-lit backlight but a light source is not disposed lateral to the light guide plate. This planar light source device includes a first light guide plate for emitting incident light from one main surface, multicolor LEDs disposed on the back surface of the first light guide plate, and multiple second light guide plates for performing color mixing of colored light rays emitted from the multicolor LEDs and guiding the resulting light to be incident on the first light guide plate.